Hvac monitoring apparatus and method

ABSTRACT

The invention relates to an HVAC monitoring apparatus. The HVAC monitoring apparatus monitors the carbon monoxide, pressure, and temperature inside the air duct network of an HVAC system, directly above the furnace. The apparatus can send detailed information wirelessly through the cloud.

FIELD OF THE INVENTION

The invention relates to an HVAC monitoring apparatus. The HVAC monitoring apparatus monitors the carbon monoxide, pressure, and temperature inside the air duct network of an HVAC system, directly above the furnace. The apparatus can send detailed information wirelessly through the cloud.

BACKGROUND OF THE INVENTION

HVAC monitoring apparatus, specifically, hazardous gas detector systems for indoor air quality monitoring, are known. See for example, U.S. Pat. No. 6,339,379, 9,030,330, 8,803,696, 6,503,141, 6,045,352, and Canadian patent application 2,921,709, all incorporated herein by reference.

It would be desirable to have an HVAC monitoring apparatus that can detect when a dirty air filter needs to be replaced. A dirty air filter reduces the oxygen air flow to the HVAC blower, burner, and heat exchanger, and reduces efficiency of the HVAC system. It would also be desirable to have an HVAC monitoring apparatus that can detect Carbon monoxide (CO) gas generation inside the furnace. It would be desirable to have an HVAC monitoring apparatus that is able to override any thermostat in the event of a hazardous gas leak. It would be desirable for such an HVAC monitoring apparatus to be able to work with any commercially available HVAC system, and thermostat, and retro-fittable onto an existing, installed HVAC system with ease. Lastly, it would be desirable for such an HVAC monitoring apparatus to be wirelessly connected to the cloud, and able to provide detailed, up to date status updates on the functioning of the HVAC system to a user on a computer, terminal, or phone connected to the cloud.

BRIEF DESCRIPTION OF THE FIGURES

Preferred embodiments are described with reference to the accompanying drawings, wherein like reference numerals indicate like parts.

FIG. 1 shows a perspective view of an embodiment of a HVAC monitoring apparatus in accordance with the present invention.

FIG. 2 shows a perspective view of the HVAC monitoring apparatus from FIG. 1 in connection with a furnace.

FIG. 3 shows a cross-sectional schematic view of the system in FIG. 2, illustrating the location of the HVAC monitoring apparatus in relation to other furnace components.

FIG. 4 shows an exploded view of one embodiment of the HVAC monitoring apparatus in accordance with the present invention.

FIG. 5 shows a perspective view of the control board in connection with the sensor control board as shown in FIG. 4, illustrating the top of the sensor control board.

FIG. 6 shows a perspective view of the control boards in FIG. 5, illustrating the bottom of the sensor control board.

FIG. 7 shows a perspective view of the HVAC monitoring apparatus from FIG. 1, illustrating the front panel of the control module housing.

FIG. 8 shows a perspective view of the backside of the front panel shown in FIG. 7.

FIG. 9 shows a perspective cross-sectional view of the HVAC monitoring system from FIG. 1.

FIG. 10 shows a perspective view of the inner tube of the coaxial tube assembly as shown in FIG. 4, illustrating the front end of the inner tube.

FIG. 11 shows a perspective view of the inner tube in FIG. 10, illustrating the backend of the inner tube.

FIG. 12 shows a perspective view of the inner tube in connection with the control module.

FIG. 13 shows a perspective view of the outer tube of coaxial tube assembly as shown in FIG. 4, illustrating the front end of the outer tube.

FIG. 14 shows a perspective view of another embodiment of the outer tube, illustrating the outer tube with axial fan configuration in connection with the control panel.

FIG. 15 shows a perspective view of the speaker module as shown in FIG. 4.

FIG. 16 shows a schematic view of the audio signal proportion through an air duct network of a house in accordance with one embodiment of the present invention.

FIG. 17 shows a perspective view of the air pressure detection module assembly as shown in FIG. 4, illustrating top of the air pressure detection module assembly.

FIG. 18 shows a perspective view of the air pressure detection module assembly as shown in FIG. 17, illustrating the bottom of the air pressure detection module assembly.

FIG. 19 shows a perspective view of the air funnel module of the air pressure detection module assembly as shown in FIG. 17.

FIG. 20 shows a perspective cross-sectional view of the HVAC monitoring apparatus as shown in FIG. 1, illustrating the positioning of the air pressure detection module assembly from FIG. 17.

FIG. 21 shows a perspective view of the air pressure detection module assembly in connection with the ambient air pressure tubing on the HVAC wire module.

FIG. 22 shows a perspective cross-sectional view of the HVAC monitoring apparatus as shown in FIG. 1, illustrating the connection of the assembly in FIG. 21 with respective to the entire apparatus.

FIGS. 23A-D show a flow chart of one possible process flow for the HVAC monitoring apparatus in accordance with the present invention.

FIG. 24 shows an elevation view of a webpage associated with a remote monitoring feature in accordance with one embodiment of the present invention, illustrating a login page.

FIG. 25 shows an elevation view of another webpage associated with the remote monitoring feature in accordance with one embodiment of the present invention, illustrating a summary screen for one HVAC monitoring apparatus in accordance with the present invention.

FIG. 26 shows an elevation view of another webpage associated with the remote monitoring feature in accordance with one embodiment of the present invention, illustrating a summary screen for multiple HVAC monitoring apparatuses in accordance with the present invention.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, is provided an apparatus for monitoring a HVAC system from a plenum of the HVAC system in which airflow generated by the HVAC system travels through, the apparatus comprising: a control module with an air inlet opening formed thereon, the control module coupled to an exterior surface of the plenum, so as to expose the air inlet opening to ambient air outside of the plenum; a probe assembly with an internal cavity, the probe assembly coupled to the control module and extending therefrom into the plenum so that the probe assembly is at least partially in a path of the airflow, wherein the internal cavity is in fluid communication with the air inlet opening; at least one sensing element is arranged within the probe assembly for monitoring at least one aspect of the HVAC airflow; and an air displacement means in fluid communication with the internal cavity; wherein the air displacement means is configured to displace air inside the internal cavity.

In certain embodiments, the probe assembly is a coaxial tube comprising an inner tube and an outer tube.

In certain embodiments, the internal cavity is defined by the space between the inner tube and the outer tube in coaxial alignment.

In certain embodiments, the sensing element is a differential air pressure sensor, which comprises a first sensor terminal configured to detect ambient air pressure outside of the plenum, and a second sensor terminal configured to detect air pressure of the airflow inside the plenum; wherein the differential air pressure sensor is configured to determine a pressure difference value between sensor data generated from the first and second sensor terminals.

In certain embodiments, the second sensor terminal is on the probe assembly and the first sensor terminal is on the control module.

In certain embodiments, the apparatus further comprises a data storage module; wherein the data storage module is configured to store the pressure difference value.

In certain embodiments, the apparatus further comprises a logic component configured to determine when a stored pressure difference value differs from a detected pressure difference value by a threshold value.

In certain embodiments, the apparatus is configured to provide a notification or visual cues when the threshold value is met.

In certain embodiments, the air displacement means draws the ambient air outside of the plenum into the internal cavity through the air inlet opening.

In certain embodiments, the sensing element is a carbon monoxide (CO) sensor for detecting CO presence within the airflow in the plenum.

In certain embodiments, the internal cavity is configured so that the air drawn into the internal cavity removes heat within proximity of the CO sensor.

In certain embodiments, the apparatus further comprises an audio module configured to emit an audio signal when the detected CO presence meets a threshold.

In certain embodiments, the audio signal is emitted into the plenum so that the audio signal is propagated through an air duct network that is in fluid connection with the plenum.

In certain embodiments, the apparatus further comprises a ultra-violet (UV) light emitter, wherein the UV light emitter is arranged to subject the airflow inside the plenum to UV light.

In certain embodiments, the apparatus further comprises a temperature sensor.

In certain embodiments, the apparatus further comprises a cover plate configured to provide a user interface comprising indicators regarding a status of the HVAC system.

In certain embodiments, the airflow from inside the plenum enters into the internal cavity through the air displacement means, thereby driving a generator operably connected to the air displacement means.

According to a further aspect of the present invention is provided a method of determining a change in air pressure by a HVAC monitoring apparatus, the method comprising: detecting a ambient air pressure outside of a HVAC plenum by a first differential air pressure sensor terminal; detecting a HVAC airflow pressure inside the HVAC plenum by a second differential air pressure sensor terminal; determining a pressure difference value between the detected ambient air pressure and the detected HVAC airflow pressure; storing the pressure difference value; continually determining a recent pressure difference value between the ambient air pressure outside the HVAC plenum and the airflow pressure inside the plenum; determining a change in air pressure by comparing the recent pressure difference value against the stored pressure difference value.

In certain embodiments, the method further comprises determining if the change in air pressure meets a predefined threshold value.

In certain embodiments, the method further comprises providing indication to user when the threshold value for pressure change is met.

According to yet a further aspect of the present invention is provided a method of providing audio warning for a HVAC system, the method comprising: generating a audio warning signal from an audio module arranged in a HVAC monitoring apparatus; directing the audio warning signal into a plenum of the HVAC system; propagating the audio warning signal through an air duct network, the air duct network is in fluid communication with the plenum.

In certain embodiments, the audio warning signal is directed into the plenum in a same direction of an airflow in the plenum.

In certain embodiments, the method further comprises emitting the audio warning signal through at least one air vent opening of the air duct network.

DETAILED DESCRIPTION

Reference is first made to FIG. 1, which shows a HVAC monitoring apparatus 10 in accordance with one embodiment of the present invention. The HVAC monitoring apparatus 10 comprises control unit 12 and probe assembly 14. In the illustrated, the HVAC monitoring apparatus 10 further includes an antenna 16.

FIGS. 2 and 3 show an installed HVAC monitoring apparatus 10 in relation to a furnace 18. A gas inlet line 20 is coupled to the furnace 18 to provide combustion fuel such as natural gas. Air is supplied via an air return duct 22, through an air filter 24 housed in an air filter compartment 23, into a blower compartment 26 which houses a blower 27 therewithin. The blower 27 forces air in the direction of a plurality of burners 28 and heat exchangers 29. Air from the blower 27 is heated by the burners 28 and heat exchangers 29, or cooled by passing through air conditioner conduits 31 and evaporator coil 33, and travels along an air supply plenum 30 into the air duct network 32 of a building. Air intake 35 provides air to the burners 28 and exhaust pipe 34 carries any combustion byproduct away from the burners 28 and heat exchangers 29 via a venting motor inside the furnace (not shown).

The HVAC monitoring apparatus 10 is installed through a perforation 36 made in the air supply plenum 30 directly above the evaporator coil 33. Optionally, it is to be appreciated that the connection between the HVAC monitoring apparatus 10 and the perforation 36 may be air tight so as to avoid unintended loss of air pressure near the HVAC monitoring apparatus 10. As shown, the control unit 12 is coupled to the exterior surface of the air supply plenum 30. The probe assembly 14 extends, through the perforation 36, into the air supply plenum 30 such that the probe assembly 14 is directly in the path of the airflow as indicated by the arrows.

Optionally, and as shown, HVAC monitoring apparatus 10 is connected to a thermostat (not shown) through thermostat wiring cable 37, and to the furnace 18 through HVAC wiring cable 39. Or, optionally, one or both of these connections may be wireless, when used with a compatible, wireless “smart” thermostat or furnace 18, respectively.

With reference to FIGS. 4 to 6, the control unit 12 comprises a control unit housing 40 and a control board 42. In the embodiment shown in FIG. 4, the control board 42 includes a thermostat terminal bank 44 located near the top of the control board for establishing electrical connection with a thermostat. The thermostat terminal bank 44 comprises a plurality of wiring terminals 46 that each receive one of a plurality of electrical control wires that are typically found in HVAC systems. A corresponding HVAC terminal bank 48 is located near the bottom of the control board 42 for establishing electrical connection with the HVAC control board which is typically located near or inside the blower compartment 26. HVAC terminal bank 48 similarly comprises a plurality of wiring terminals 46. The control board 42 is configured such that commands issued by the thermostat may be passed onto the furnace 18 through the control board 42. When required, the control board 42 may interrupt or override the thermostat control signals and issue its own control signals to the furnace 18 as described in more detail below.

In the illustrated embodiment, four control board LED's 50 situated on the control board 42 and may be used to confer information regarding the status of the furnace 18 or the HVAC monitoring apparatus 10. It may be appreciated that the number of LED's could vary based on the information to be provided to users. The LED 50's may be of different color to provide visual cues to users regarding the status of the furnace 18.

With reference to FIGS. 4 and 7 to 9, in certain embodiments, and as shown, control unit housing 40 is essentially circular in shape with a front panel 52 that has a back side 54. A side wall 56 is formed along the peripheral edge of the front panel 52 extending from the back side 54. Near the top of front panel 52 is a thermostat wiring terminal opening 58 which provides access to thermostat terminal bank 44 positioned underneath. Similarly, near the bottom of front panel 52 is a HVAC wiring terminal opening 60 to provide access to the HVAC terminal bank 48.

As shown, a plurality of front panel LED openings 62 are formed through the front panel 52 such that the openings permit unimpeded view of control board LEDs 50 beneath. Optionally, though not shown, these openings may be covered by a clear or translucent material, to prevent dust entry. In the embodiment best shown in FIG. 8, to minimize an illuminating LED 50 from being viewable in an adjacent LED opening 62, a hollow cylindrical front panel LED tubing 64 is formed extending from each front panel LED opening 62 on the front panel back side 54. When assembled, each LED tubing 64 is positioned directly above a control board LED 50. This way, light emitted from a particular LED 50 may be shielded from view through the adjacent LED openings 62.

A calibration button 66 is also located on the front panel 52. In the illustrated embodiment, the calibration button 66 is in the form of a tactile button that is commonly known in the art with a projection 68 extending from back side 54. The projection 68 is to be positioned directly above corresponding control logic on control board 42, and may be utilized to initiate tasks such as filter calibration by storing sensor measurements as described in more detail below. Other functionalities may also be performed using the button.

In some embodiments, a thermostat wire tubing opening 70 is formed near the top of the side wall 56 of control unit housing 40, and is configured to receive a thermostat wire module 72. The thermostat wire module 72 is formed by a plurality of hollow cylindrical wire tubing 74 extending vertically from a base plate 76. The thermostat wire tubing opening 70 comprises a recessed groove 77 with a groove opening 78 as best shown in FIG. 4. The groove opening 78 is configured to receive the plurality of wire tubing 74 of the thermostat wire module 72 with the base plate 76 fitting into the recessed groove 77. Once the thermostat wire module 72 is inserted into the thermostat wire tubing opening 70, the plurality of wiring tubing 74 are positioned directly over the wiring terminals 46 in the thermostat terminal bank 44. Each wire tubing 74 is dimensioned to receive one of the electrical connection wires with the thermostat. By isolating the electrical connection wires using wire tubing 74, the chances of electrical shorts amongst the wires may be minimized. The wire tubing 74 may further serve to guide individual electrical connection wires into the corresponding wiring terminals 46 on the control board 44 to facilitate easier installation.

As shown, near the bottom of control unit housing side wall 56 is a HVAC wire tubing opening 80 configured similar to the thermostat wire tubing opening 70 described above, and is configured to receive a HVAC wire module 82. The HVAC wire module 82 is essentially similar in construction as the thermostat wire module 72, but with an added ambient air pressure opening (not shown) formed through its base plate 83 and extending therefrom is an ambient air pressure tubing 84 as best shown in FIG. 8.

In some embodiments, four control unit thermocooling openings 86 are formed throught the peripheral edge of the front panel 52. The thermocooling openings 86 are dimensioned to permit unimpeded air flow for cooling purposes as described in more detail below. Those skilled in the art would readily appreciate that the number, size, and location of the openings may vary based on cooling needs. On the back side 54 of front panel 52, thermocooling projections 88 are formed extending from each thermocooling opening 86 to facilitate air flow from the thermocooling openings 86 into the cooling cavity described in more detail below. In some embodiments, mounting plates 90 are formed on the base plates of wire modules 72 and 82 for connecting with the probe assembly 14 as best illustrated in FIG. 9. As may be obvious to those skilled in the art, other mounting mechanisms may be used.

In embodiments with wireless communication capability, antenna 16 is connected, through an antenna opening 91 on the control unit housing sidewall 56 as shown in FIG. 8, to the corresponding control logic components (such as a wifi-module) on the sensor control board 106. It may be appreciated that the physical location of the wifi control logic component is not limited to the illustrated embodiments and may be located on either control board 42 or 106. The antenna 16 may enable wireless connection with a router situated in a building to establish communication with remote servers. The antenna 16 may also enable wireless connection with the furnace 18 and/or the thermostat, in cases, for example, where a compatible “smart” thermostat is used. This may, in some embodiments, make hard wire connections redundant and unnecessary. Conversely, in certain embodiments, for example, where the furnace room in which the furnace 18 is installed does not obtain proper wireless signal coverage, relevant messages or signals can be sent to a wi-fi enabled “smart” thermostat through the existing thermostat wiring cable 37, or through separate, dedicated wiring (not shown), for transmission of said signals, by the thermostat, to the cloud or to an external user or maintenance operator.

FIG. 4 shows one embodiment of the present invention which further includes a user interface cover 92 that is configured to be coupled over the front panel 52 of the control unit housing 40. The user interface cover 92 may be operable to provide a simple and user-friendly interface for users to readily discern information about the furnace 18. In the illustrated embodiment, four interface cover LED openings 94 are defined through user interface cover 92 and are configured to be in alignment with front panel LED openings 62 such that the control board LED 50 beneath are readily viewable through the interface cover LED openings 94. It is to be appreciated that the number of openings could vary based on the amount of information the HVAC monitoring apparatus 10 may convey. Optionally (not shown) interface cover LED openings 94 can be covered in clear or translucent material such as a clear plastic, to prevent dust entry but allow light transmission.

As shown, text labels 96 are printed beneath each LED opening 94 to identify the information indicated by the corresponding LED. In the depicted embodiment, labels “NORMAL”, “CAUTION”, and “CRITICAL” may be used to indicate the operational status and/or the CO levels of the furnace 18, and “SERVICE” is used to indicate maintenance action, such as replacing filter, may be required.

On user interface cover 92, a number of interface cover cooling openings 98 are provided which correspond in size and location to the control unit thermocooling openings 86 on the control unit housing front panel 52. Openings 98 function to permit air to enter the HVAC monitoring apparatus 10 for cooling.

The user interface cover 92 may be coupled to the front panel 52 of the control unit housing front panel 52 via any suitable mounting mechanism such as screws, bolts, adhesive, etc. In one embodiment, the user interface cover 92 is magnetically coupled to the front panel 52. In such embodiments, the user interface cover 92 may be easily removed without the need for additional tools, thus providing easy access to the front panel 52 for installation or calibration purposes.

Also in the illustrated embodiment is a level 100, which is coupled to the back side 54 of control unit housing 40 by being held in place by two clips 102. The level 100 is visible from a level opening 104 on the front panel 52. Level 100 may be operable to assist to ensure the HVAC monitoring apparatus 10 is positioned such that the sensors are properly oriented during installation.

In the embodiment shown in FIG. 4, the probe assembly 14 comprises a sensor control board 106 and a coaxial tube assembly 108. In the embodiment shown in FIGS. 5, a speaker 110 and carbon monoxide (CO) sensor 112 are mounted on the top surface of the sensor control board 106. As shown in FIG. 6, an differential pressure sensor 114with two sensor terminals 115 is mounted on the underside of the sensor control board 106. The probe assembly 14 also comprises a temperature sensor (not shown). It may be appreciated by those skilled in the art that other types of sensors, such as carbon dioxide (CO₂) sensor, methane sensor, radon sensor, air quality sensor, bacterial sensors, and any other suitable sensors, may also be added to the sensor control board 106.

As can be appreciated, sensor control board 106 may also house a back-up power supply (for example, a rechargeable battery or a capacitor) which allows the system to work and/or retain memory state even when power is out.

With reference now to FIGS. 4 and 10 to 12, the coaxial tube assembly 108 comprises an inner tube 116 and an outer tube 118. The inner tube 116 has an elongated tubular body 120 having a diameter 122 sufficient to accommodate the sensor control board 106 therein. An inner tube flange 124 is formed at the proximal end of the body 120. The inner tube flange 124 is sized to fit into the back of control unit housing 40 as best shown in FIG. 12. In some embodiments, two positioning cutouts 126 are formed on the flange 124, and are configured to receive corresponding positioning bosses from the outer tube flange. Four inner tube thermocooling openings 128 for permitting air flow are also formed on flange 124. The openings 128 correspond in size, number, and location to the cooling openings 86 and 98 in the control unit housing 40 and user interface cover 92, respectively.

An inner tube speaker opening 130 is formed near the top of inner tube body 120. The speaker opening 130 is positioned directly above the speaker 110 on the sensor control board 106. In the illustrated embodiment, two speaker module connection bosses 132 flank the speaking opening 130. The height of the speaker module connection boss 132 is approximately the difference in diameter between the inner and outer tubes 116 and 118. Thus, in addition to providing a point of connection, the connection bosses 132 may also serve to provide structural support for the outer tube 118 when in coaxial alignment.

Two air pressure detection assembly connection bosses 134 are formed near the bottom surface of the inner tube body 120 as shown in the FIG. 11. The height of the air pressure detection assembly connection bosses 134 is similar to that of the speaker module connection bosses 132, and may also provide additional structural support for the outer tube 118 when in coaxial alignment with inner tube 116. An air pressure detection opening 136 is located in between the two air pressure detection assembly connection bosses 134.

FIGS. 13 and 14 show embodiments of the outer tube 118 in accordance with the present invention. As shown, outer tube 118 has an essentially elongated tubular body 138 with a diameter 140. As the probe assembly 14 will be inserted into the airflow path of the furnace 18, the circular body shape may serve to minimize resistance to airflow and thus minimize disruptions in airflow of the furnace 18. The outer tube body diameter 140 is larger than the inner tube body diameter 122. An outer tube body flange 142 is formed on the proximal end of the outer tube body 138. On the flange 142, two positioning bosses 144 are located which are configured to fit into inner tube flange positioning cutouts 126. When positioning bosses 144 are inserted into positioning cutouts 126 on the inner tube body flange 124 and secured with an appropriate mounting mechanism such as a screw, the fit between cutouts 126 and the position bosses 144 prevents relative rotation between the inner and outer tubes 116 and 118, and may further help to maintain the coaxial alignment between the inner and outer tubes. It may be appreciated that other positioning elements, such as positioning inserts, may also be used.

A recessed speaker module groove 146 with a central orifice 148 is formed near the top portion of the outer tube body 138. The orifice 148 is aligned with the inner tube speaker opening 130 as well as the speaker 110 on the sensor control board 106. In conjunction with the inner tube speaker opening 130, the speaker module groove 146 is configured to receive a speaker module 150 as shown in FIG. 15.

In one embodiment, the speaker module 150 is an essentially inverted conical structure with a hollow center and openings on either end. The speaker module 150 includes a first body portion 152 and a second body portion 154 of a smaller diameter than the first body portion. The first and second speaker module body portions 152 and 154 are separated by a shoulder 156. At the free end of the first body portion 152, a speaker module flange 158 is formed. As shown, flange 158 also has two screw holes 160 for mounting purposes. As best shown in FIG. 7, the second body portion 154 of the speaker module 150 is inserted through inner tube speaker opening 130 such that the opening on the free end of the second body portion 154 rests immediately above the speaker 110. Shoulder 156 of the speaker module rests upon the exterior surface of inner tube body 120. The speaker module flange 160 sits within the recessed speaker module groove 146 on the outer tube with the first body portion 152 of the speaker module 150 inserted into the space between the outer tube 118 and inner tube 116. The speaker module 150 is secured onto the coaxial tube assembly 108 through two screws 162 each screwed into a respective inner tube speaker module connection boss 132. It may be appreciated by those skilled in the art that other forms of connection may be possible. It may be further appreciated by those skilled in the art that filters may be positioned between the first body portion 152 and second body portion 154 to minimize dust entry.

The speaker module 150 may be operable to ensure a continuous sound propagation continuum from the speaker 110 into the air supply plenum 30. In a preferred embodiment, the speaker module 150 is located at the top of the probe assembly 14 as shown in the figures such that any sound emitted from speaker 110 would travel in the same direction as the HVAC air flow which may assist in carrying the sound along the air duct network 32. As illustrated in FIG. 16, the air duct network 32, which likely extends to every room of a house, may assist in propagating any warning messages generated by the HVAC monitoring apparatus 10 throughout the house. By way of a non-limiting example, if a CO leak is detected by the HVAC monitoring device 10 and an audio warning signal is emitted, the warning audio signal may be propagated, through the air duct network 32, into every room of the house and emitted out of very air vent grill or register. This way, the inhabitants in the house will be more likely to receive the warning and take appropriate action regardless of their physical location in the house or proximity to the HVAC monitoring apparatus 10.

Near the bottom of the outer tube body 138, an outer tube air pressure detection opening 162 is aligned with the inner tube air pressure detection opening 136, and is positioned immediately below the differential pressure sensor 114 on the underside of the sensor control board 106. The outer tube air pressure detection opening 162 is configured to receive an air pressure detection module assembly 164, an embodiment of which is shown in FIGS. 17 to 21. With reference to these figures, the air pressure detection modules assembly 164 comprises a base module 166 as shown in FIG. 18 and an air funnel module 168 as shown in FIG. 19. In the illustrated embodiment, base module 166 includes an arcuate base plate 170 with curvature matching that of the outer tube body 138. On the top surface nearing one end of the base plate 170, there is formed a raised seating 172 for receiving and connecting to the air funnel module 168. It may be appreciated that, to minimize dust entry, a filter (not shown) may be attached in between seating 172 and the air funnel module 168. A central orifice 174 permits airflow from the furnace 18 to enter. Three connection holes 176 are formed along the circumferential perimeter of the seating 172 around the central orifice 174. Plate connection holes 178 are formed on both ends of the base plate 170 so that the air pressure detection module assembly 164 may be secured to the inner tube air pressure detection assembly connection bosses 134 on the bottom side of the inner tube 116 as shown in FIG. 7.

The air funnel module 168 as shown in FIG. 19 includes an essentially cylindrical body 180 with a central bore 182 defined by an interior wall 184. On the top surface of the cylindrical body 180, extending from the central bore 182, is a tubing 186 with smaller diameter compared to the central bore 182 so as to focus air flow into a narrowed opening 188. The bottom surface of the cylindrical body 180, three connection bosses 190 are configured to fit into the base module connection holes 176. An air sampling opening 192 is formed in the cylindrical body 180 next to the tubing 186 such that both are positioned directly above the base plate central orifice 174 when mounted.

As shown in FIGS. 4, 9 and 18, when the air pressure detection module assembly 164 is mounted, the tubing 186 enters the interior of the inner tube 116 through inner tube air pressure detection opening 136 such that tubing opening 188 is positioned over one of the two sensor terminals 115. Any HVAC air flow that enters from the central orifice of the air pressure detection module assembly is guided, through tubing 186 and directed to the sensor terminal 115 connected thereto.

In order to detect air pressure change, a constant air pressure value is needed to serve as the base value against which the detected air pressure readings are compared. Thus, as shown in FIG. 21, an ambient pressure sensing tubing 194 connects the other air pressure sensor terminal 115 to the ambient air pressure tubing 84 located on the HVAC wire module 82. Thus, the differential pressure sensor 114 may be operable to detect the ambient air pressure outside of the air supply plenum 30 through the ambient air pressure tubing 84 located at the bottom of the control unit housing 40. Concurrently, a reading of the air pressure exerted by the HVAC system generated air flow inside the air supply plenum 30 is also taken through the air pressure sensor terminal 115 connected to the air pressure detection module assembly 164. Upon initial installation or replacing an air filter 24, the HVAC monitoring apparatus 10 may be calibrated by pressing the calibration button 66 on the control unit 12 such that the initial air pressure differential between the ambient air pressure and the HVAC air flow is stored on one of the two control boards 42 and/or 106. The HVAC monitoring apparatus 10 then could continually or periodically, measure the air pressure differential at a specific point in time and compare that air pressure differential value against the initially stored air pressure differential value to determine if there has been a change in air pressure differential value. By way of a non-limiting example, should the air pressure differential reading be less than the initial differential value, it is likely indicative of a partially blocked filter. If the difference in air differential pressure meets a certain threshold then indication may be provided to the end user that air filter 24 needs to be replaced. As discussed below, the air pressure differential value may also be used in other ways to provide useful information regarding the HVAC system.

As it may be known to those skilled in the art, typical CO sensors are sensitive to air pressure changes. In accordance with some embodiments of the present invention, the CO sensor 112 is placed away from the air pressure detection module assembly 164 so as to avoid direct air flow. As best seen in FIGS. 9 and 20, the air funnel module Air sampling opening 192 permits air from inside the air supply plenum 30 to enter into the air space in between the sensor control board 106 and the bottom portion of the inner tube 116. Sensor control board perforations 196 are formed directly beneath the CO sensor 112. According to this embodiment, once the air generated by the HVAC system enters the HVAC monitoring apparatus 10 through air funnel module CO air flow opening 192, the air may slowly diffuse through the perforations 196 and become detectable by the CO sensor 112.

It is also known that CO sensors are typically fluid based and are prone to problems caused by the evaporation of chemical fluid in high temperature environments. In one preferred embodiment of the present invention, a cooling system is implemented to cool the control boards and the sensors thereon to at least partially minimize the likelihood of fluid evaporation in the CO sensor. In addition, CO sensors that do not employ chemical fluid may have a relatively low heat tolerance. Thus, the cooling system implemented in the present invention may also allow such sensors to be used and function as intended.

As disclosed above, outer tube body diameter 140 is greater than the inner tube body diameter 122 such that, when in coaxial alignment, a space is formed between the two tubes. The space serves as cooling cavity 198 where air may enter into the cooling cavity 198 through inner tube cooling openings 128. Cooling cavity 198 terminates at the distal end of the inner tube 116 where, in one embodiment and as shown, a suction fan 200 resides at the distal end of the outer tube body 138. Portions of the coaxial tube assembly 108 on top of the fan 200 opens to an outer tube exhaust opening 204. A cooling exhaust module 206 as shown in FIGS. 4, 7 and 22 may be coupled to the cooling opening 204 to facilitate exhaust air flow from the fan 200 to the exhaust opening 204. The suction fan 200 operates to draw air from outside of the HVAC supply plenum 30 into the cooling cavity 198 through cooling openings 128 on the inner tube. It may be appreciated that filters (not shown) may be mounted to the cooling openings 128 to minimize dust entry. The air, by convection and conduction, carries excess heat that was generated by the sensor control board 106 and heated HVAC airflow from the exterior surface of the inner tube body 120 towards suction fan 200 along the cooling cavity 198 and expelled, preferably in the same direction as the HVAC system airflow through the top opening of the cooling exhaust module 206, or alternatively, for example, perpendicularly thereto. By way of a non-limiting example, FIG. 14 shows an embodiment where the outer tube 118 is configured to accommodate an axial fan where the exhaust is expelled from the distal end of the outer tube 118.

As it may be appreciated, in certain embodiment of the present invention, the suction fan 200 and its motor may function as a generator. By way of a non-limiting example, airflow from the HVAC system may be directed into the back of the HVAC monitoring apparatus 10 where a number of air openings 208 may be formed on the distal end of the outer tube body 138 as shown in FIG. 14. The air will rotate fan blades of the suction fan 200, which in turn rotates the motor and allow the motor to become a generator that is capable of generating electrical current that may be used by the on board electronics in the HVAC monitoring apparatus.

As may also be appreciated, in a similar manner, airflow from the furnace may be used, for example, to cause a pressure differential (vacuum effect), to draw air from control unit thermocooling openings 86, through cooling cavity 198 and out into the HVAC system airflow. Alternatively, in a further embodiment, a venturi tube may be used to utilize the airflow from the furnace to cause a pressure differential by the “venturi effect” within the venturi tube to draw air from control unit thermocooling openings 86, through cooling cavity 198.

In another embodiment, a ultra-violet (UV) light emitter may be coupled to the probe assembly 14 such that any HVAC air flow may be subjected to UV light treatment to reduce the amount of microbial contaminants.

In certain embodiments, EMI shielding (not shown) may be used to protect sensors and other sensitive electronic components from the EMI emissions naturally generated by the furnace 18.

In use, the HVAC monitoring apparatus 10 can perform various advantageous tests and system controls. Examples of such tests and controls are described below.

Filter Health

In certain embodiments, the HVAC monitoring apparatus 10 can determine when the air filter 24 needs to be changed by user, and can alert the user of this. When an air filter 24 is changed, a user will “reset”, or notify, the HVAC monitoring apparatus 10. This can be done by depressing calibration button 66 for a defined period of time, or through a software interface (for example, a phone app) connected via wifi to the HVAC monitoring apparatus 10. The HVAC monitoring apparatus 10 will set a baseline pressure differential in the system, by (optionally) turning on the blower 27 of the furnace 18 and measuring the air pressure differential between the inside and the outside of the plenum 30, utilizing the two ports of the differential pressure sensor, one measuring inside the plenum 30 and the other measuring ambient air pressure through tubing 84. The HVAC monitoring apparatus 10 will then take continuous or (preferably) intermittent differential pressure readings. A change in differential pressure reading (i.e. a decrease in plenum 30 pressure as compared to ambient air pressure) greater than a certain, defined, amount, will suggest the filter 24 needs to be changed. The HVAC monitoring apparatus can alert a user of this, using the control board LED 50, the speaker 110, a signal sent to the smart thermostat, or a message sent wirelessly to a phone app. Optionally, the signal can be sent to an HVAC maintenance professional as well.

Note that, since differential pressure readings are being taken on a regular basis, the gradual decrease in differential pressure can be measured and used as further information on the health of the furnace 18. Utilizing machine learning algorithms and big data analysis, this information can be combined with the data obtained from a plurality of HVAC monitoring apparatus 10 in different homes, to determine and optimize, for example, the threshold for when a user is notified that filter 24 needs to be changed. Such data can also be used to identify outliers (for example, HVAC systems 18 that have increased need for filter changes) and identify and signal the need for a service call.

As could be appreciated, the HVAC monitoring apparatus 10, when equipped with wireless communications, can communicate with remote sensors, such as sensors placed at or in air duct registers, which would be useful for monitoring the air actually entering a room. The HVAC monitoring apparatus 10 can also communicate with sensors in or around a water heater or boiler, a fireplace, an oven, a sump pump, smoke detectors, or in an air conditioning unit, for example, and send such information to a user in an integrated fashion as otherwise herein described. For example, the HVAC monitoring apparatus 10 can be in wireless communication with a fireplace-situated carbon monoxide detector, and send an alert to a user or (for example) a fire department if CO levels are high in the fireplace.

Carbon Monoxide Sensing

In certain embodiments, the HVAC monitoring apparatus 10 can sense CO levels within the plenum 30. This is significantly advantageous over traditional CO sensors which are monitoring room levels, since it senses at the source of the CO, and can thus establish the presence of CO earlier. It would be appreciated that CO levels generated in the furnace 18 would be at their most concentrated in the plenum 30 rather than in rooms being heated by the furnace 18, and therefore a CO sensor within the plenum 30 should lead to earlier detection of CO. The HVAC monitoring apparatus can continuously sense for CO level, or it can do so intermittently, for example, once every minute. Depending on the level of CO, the HVAC monitoring apparatus 10 can have several, escalating, alerts. For example, at a low but measurable level of CO, the HVAC monitoring apparatus 10 may inform a user through control board LEDs 50, or through a signal sent wirelessly to an HVAC maintenance professional. At a higher level of CO (as may be defined by common industry standards such as CSA, UL, ASHRAE), the HVAC monitoring apparatus 10 may send a signal through speaker 110, which will resonate through the plenum 30. At an even higher level of CO, the HVAC monitoring apparatus 10 may override the signal sent from the thermostat, and shut down furnace 18, either for a defined period of time to allow the CO to dissipate, or until a manual reset of the system is performed to ensure maximum safety. In an alternative embodiment, at high levels of CO, the HVAC monitoring apparatus 10 may override the signal sent from the thermostat, shutting down the burners 28 of the furnace 18, but turning on the furnace 18 blower 27, to attempt to dissipate the CO. In certain embodiments, the HVAC monitoring apparatus 10 will continue to monitor CO even after shutting down the furnace 18. In certain embodiments, the HVAC monitoring apparatus 10 will increase the frequency at which it measures CO when an elevated level of CO is sensed. In certain embodiments, the HVAC monitoring apparatus 10 will continuously forward CO information to a user and/or HVAC maintenance professional and fire department, through for example a phone app and/or online dashboard. Moreover, detection of CO is not only shown by the LEDS and app/dashboard notifications, but audio alarm signals' frequency also increase with higher levels of CO.

Detection of Frozen Coil

In certain embodiments, the HVAC monitoring apparatus 10 can be used to detect a frozen air conditioning conduit 31 and/or evaporator coil 33. Frozen air conditioning conduits are a common furnace 18 problem. Sometimes due to improper drainage, over use of the air conditioning system and coils, low gas/coolant levels, or improper blower activity, air conditioning conduit 31 and evaporator coil 33 may become frozen or blocked. This is often referred to in the industry as a “frozen coil”. In the case of a frozen coil, typically, the temperature in the air supply plenum directly above the conduit 31 and evaporator coil 33 will decrease significantly, and there will be a fairly sudden and dramatic decrease in air flow through the plenum 30. When the HVAC monitoring apparatus 10 senses this combination of events, it can signal a user, again, through lights, sound, or a wireless signal, that the coil is likely frozen. The HVAC monitoring apparatus 10 can also attempt to fix the problem, by turning off the air conditioning, and activating the burners 28 (something you wouldn't typically do in seasons where the air conditioner is being used) to melt the frozen air conditioning conduit 31.

Detection of Short Cycling

In certain embodiments, the HVAC monitoring apparatus 10 can also be used to detect the “short cycling” of an furnace 18. This is, again, a fairly common HVAC problem which typically requires servicing. Symptoms of a short cycling problem, such as a dramatic increase in temperature in the plenum 30 and shorter on-off periods of the heating system, and cycling air pressure readings, can be identified by the HVAC monitoring apparatus 10 as a short cycling problem. Short cycling typically requires servicing of the furnace 18, so in a preferred embodiment, the HVAC monitoring apparatus 10 will automatically signal, via wifi, an HVAC maintenance professional.

Power Outage

In certain embodiments, since the HVAC monitoring apparatus 10 is connected to both the thermostat and the furnace 18, it can easily identify, and signal to a user, power outages in either. Alternatively, the HVAC monitoring apparatus 10 can identify power outages in the furnace 18 due to lack of air pressure differential. This may be useful to seasonal users of a property, for example.

High Limit Switch Failure

In certain embodiments, the HVAC monitoring apparatus 10 can be utilized as a backup to the high limit switch found in most furnaces. The high limit switch is a furnace safety switch, which shuts down the HVAC system 10 if the temperature hits a high limit. In the case of a high limit switch failure (which is rare but can be quite dangerous) the HVAC monitoring apparatus 10, sensing temperature in the plenum 30 above the high limit, is able to shut down the HVAC system 10, and, again, alert a user or HVAC maintenance professional.

Pressure Switch Failure

Similarly to the High Limit Switch Failure, in certain embodiments, the HVAC monitoring apparatus 10 can be utilized as a backup to the high pressure switch found in most furnaces. In the case of a high pressure switch failure, the HVAC monitoring apparatus 10, sensing abnormal temperatures, pressures, and gas levels inside the duct, the HVAC monitoring apparatus 10 can monitor radical or elevating changes in the behavior of the furnace and can associate those changes with the pressure switch failure, is able to shut down the HVAC system 10, and alert a user or HVAC maintenance professional.

System Maintenance Tests

In certain embodiments, the HVAC monitoring apparatus 10 can perform active testing of the furnace 18. For example, the HVAC monitoring apparatus 10 may perform a period testing of various components of the furnace 18. Alternatively, the HVAC monitoring apparatus 10 can be wirelessly directed to perform such testing. For example, if a user calls an HVAC maintenance professional with a problem, the HVAC maintenance professional may be able to diagnose the problem remotely, by directing the HVAC monitoring apparatus 10 to perform certain tests of the furnace 18. The HVAC monitoring apparatus 10 is wired to the furnace 18, and can override thermostat control to easily perform such tests.

For example, the blower 27 may be tested, by turning the blower 27 on and off, and measuring pressure differential. The heating system can be tested, by turning on the blower 27 and the burners 28, and measuring pressure differential and temperature. Additionally, the cooling system may also be tested, by turning on the air conditioning system and the blower motor 27. In HVAC systems 18 with two stage burners, the two separate burner stages may also be tested to determine which is at fault. The HVAC monitoring apparatus 10 can similarly determine a failure to switch to second stage (a common problem of HVAC systems 18), the efficiency of each stage (by measuring temperatures and pressures over time, for example), and whether cycle times are within normal operating parameters.

Similarly, pilot light problems can be tested, by triggering the burner 28 and monitoring the resulting pressure differentials and temperatures or lack thereof to determine a pilot light problem.

FIGS. 23A-D show a flow chart of one example of a possible process flow for HVAC monitoring apparatus 10. The HVAC monitoring apparatus 10 powers up 210 and runs through its definitions 212 and set up 214. The sensors are calibrated 216 and compared against references 218. The temperature sensor is activated 222 and the temperature data is sent 224 wirelessly to a web server 236. The carbon monoxide sensor is then activated 226 and the carbon monoxide data is sent 228 wirelessly to a web server 236. The pressure sensor is then activated 230 and the pressure data is sent 232 wirelessly to the web server 236.

The temperature is then sampled 234 by the temperature sensor. If the temperature in the plenum 30 is greater than 85 degrees Celcius, a series of actions are initiated 238, 246. The HVAC monitoring apparatus 10 turns on its fan 200, and signals the furnace 18 to turn on the blower 27, turn off the burners 28, and to shut down. Finally, the yellow LED on the HVAC monitoring apparatus 10 is turned on, and optionally (not shown) the user is alerted via phone app. If the temperature in the plenum 30 is between 30 degrees Celcius and 85 degrees Celcius, the HVAC monitoring apparatus 10 fan 200 is turned on. If the temperature in the plenum is between 5 degrees Celcius and 30 degrees Celcius, the HVAC monitoring apparatus fan 200 is turned off. If the temperature in the plenum is below 5 degrees Celcius, a series of actions are initiated 244, 252. The HVAC monitoring apparatus fan 200 is turned off; the furnace is turned off; the furnace fan is turned off; a shutdown signal is turned on; the yellow LED on the HVAC monitoring apparatus is turned on, and optionally (not shown) the user is alerted via phone app.

Next, the carbon monoxide sensor is read 254. If the average CO level is greater or equal to 400 ppm 256, a series of actions are initiated 266. If the average CO level is greater or equal to 400 ppm for more than 4 minutes, an alarm is sounded every second (speaker 110 is activated); if it is greater or equal to 400 ppm for more than 15 minutes, the HVAC monitoring apparatus 10 signals a shutdown of the furnace 18. If the average CO level is between 150 and 400 ppm 258, a series of actions are initiated 268. If the average CO level is within this range for more than 10 minutes, an alarm is sounded (speaker 110 is activated) every 3 seconds; if it is within this range for more than 50 minutes, the HVAC monitoring apparatus 10 signals a shutdown of the furnace 18. If the average CO level is between 70 and 150 ppm 260, a series of actions are initiated 270. If the average CO level is within this range for more than 60 minutes, an alarm is sounded (speaker 110 is activated) every 5 seconds; if it is within this range for more than 240 minutes, the HVAC monitoring apparatus 10 signals a shutdown of the furnace 18. If the average CO level is between 30 and 70 ppm 262, a series of actions are initiated 272. If the average CO level is within this range for more than 30 days, an alarm is sounded (speaker 110 is activated) every second. If the average CO level is less than 30 ppm 264, no alarm is sounded and the furnace 18 continues normal operation 274. Alternatively, the time to shutdown can also be made to occur without delay after CO detection.

The system is then checked for a drop in pressure 276. Optionally, a user or a HVAC technician is alerted.

FIGS. 24-26 show one possible embodiment of the remote monitoring of the HVAC monitoring apparatus 10. FIG. 24 shows a possible login screen 287, where a user or a HVAC technician would log onto the system. FIG. 25 shows a summary screen for one HVAC monitoring apparatus 10, showing the condition of the furnace 18 on which the HVAC monitoring system 10 is affixed. Shown is a chart of temperature over time 288, duct pressure over time 290, and carbon monoxide level over time 292, for rapid visual confirmation of the health of the system. Also shown is a summary of the efficiency of the furnace 293 as determined by the HVAC monitoring system 10, a summary of the carbon monoxide level 294, the status of the filter 296, whether the HVAC blower 27 is on 298, whether the air conditioning is on 300, and whether the furnace is on 302. A general summary of the status of the HVAC system 306 is also shown, as is the location of the HVAC system 304. Further information regarding the HVAC system 10 can also be seen, including the name of the customer, the type and model of the furnace and air conditioning, and the model and other information regarding HVAC monitoring system 10 installed thereon. As can be seen, the one screen nicely enables an HVAC technician to rapidly see the status of the HVAC system 10, diagnose problems, and order parts, etc. FIG. 26 shows a summary screen for multiple HVAC monitoring systems 10. For each HVAC monitoring system 10, summary information including the HVAC status 306, the status of the furnace 302, Air Conditioning system 300, blower 298, filter 296, carbon monoxide level 294, and general efficiency 293 is shown. In another embodiment, carbon dioxide sensors can monitor for greenhouse gas emissions and efficiency—to supplement other sensors such as pressure and temperature. HVAC systems needing maintenance or attention are easily seen as highlighted 308. This allows an HVAC technician to quickly determine which HVAC systems need attention. Clicking on any line of this summary information screen will provide the detailed information as previously shown in FIG. 25.

As can be appreciated, the detailed information provided can help optimize the efficiency of the HVAC system, by alerting a user or technician when the HVAC system is not working optimally, by alerting when filters need to be changed, and by modifying the starting, stopping and duration of running of the furnace based on efficiency data received by, for example, the temperature and pressure sensors. Data from a plurality of HVAC monitoring apparatus, in different homes, can be compiled and used for macro analytics, and, with machine learning algorithms, thresholds for alerts, shut down times, etc., can be optimized with use. 

1. An apparatus for monitoring a HVAC system from a plenum of the HVAC system in which airflow generated by the HVAC system travels through, the apparatus comprising: a control module with an air inlet opening formed thereon, the control module coupled to an exterior surface of the plenum, so as to expose the air inlet opening to ambient air outside of the plenum; a probe assembly with an internal cavity, the probe assembly coupled to the control module and extending therefrom into the plenum so that the probe assembly is at least partially in a path of the airflow, wherein the internal cavity is in fluid communication with the air inlet opening; at least one sensing element is arranged within the probe assembly for monitoring at least one aspect of the HVAC airflow; and an air displacement means in fluid communication with the internal cavity; wherein the air displacement means is configured to displace air inside the internal cavity.
 2. The apparatus of claim 1, wherein the probe assembly is a coaxial tube comprising an inner tube and an outer tube.
 3. The apparatus of claim 2, wherein the internal cavity is defined by the space between the inner tube and the outer tube in coaxial alignment.
 4. The apparatus of claim 1, wherein the sensing element is a differential air pressure sensor, which comprises a first sensor terminal configured to detect ambient air pressure outside of the plenum, and a second sensor terminal configured to detect air pressure of the airflow inside the plenum; wherein the differential air pressure sensor is configured to determine a pressure difference value between sensor data generated from the first and second sensor terminals.
 5. The apparatus of claim 4, wherein the second sensor terminal is on the probe assembly and the first sensor terminal is on the control module.
 6. The apparatus of claim 3, further configured to determine when a stored pressure difference value differs from a detected pressure difference value by a threshold value.
 7. The apparatus of claim 6, wherein the apparatus is configured to provide a notification or visual cues when the threshold value is met.
 8. The apparatus of claim 1, wherein the air displacement means draws the ambient air outside of the plenum into the internal cavity through the air inlet opening.
 9. The apparatus of claim 1, wherein the sensing element is a carbon monoxide (CO) sensor for detecting CO presence within the airflow in the plenum.
 10. The apparatus of claim 10, wherein the internal cavity is configured so that the air drawn into the internal cavity removes heat within proximity of the CO sensor.
 11. The apparatus of claim 10, further comprising an audio module configured to emit an audio signal when the detected CO presence meets a threshold.
 12. The apparatus of claim 10, wherein the apparatus shuts down the HVAC system when the detected CO presence meets a threshold.
 13. The apparatus of claim 11, wherein the audio signal is emitted into the plenum so that the audio signal is propagated through an air duct network that is in fluid connection with the plenum.
 14. The apparatus of claim 1, which further comprises a ultra-violet (UV) light emitter, wherein the UV light emitter is arranged to subject the airflow inside the plenum to UV light.
 15. The apparatus of claim 1, further comprising a temperature sensor.
 16. The apparatus of claim 1, wherein the airflow from inside the plenum enters into the internal cavity through the air displacement means, thereby driving a generator operably connected to the air displacement means.
 17. A method of determining a change in air pressure by a HVAC monitoring apparatus, the method comprising: detecting a ambient air pressure outside of a HVAC plenum by a first differential air pressure sensor terminal; detecting a HVAC airflow pressure inside the HVAC plenum by a second differential air pressure sensor terminal; determining a pressure difference value between the detected ambient air pressure and the detected HVAC airflow pressure; storing the pressure difference value; continually determining a recent pressure difference value between the ambient air pressure outside the HVAC plenum and the airflow pressure inside the plenum; determining a change in air pressure by comparing the recent pressure difference value against the stored pressure difference value.
 18. The method of claim 17, further comprising determining if the change in air pressure meets a predefined threshold value.
 19. The method of claim 18, further comprising providing indication to user when the threshold value for pressure change is met.
 20. A method of providing audio warning for a HVAC system, the method comprising: generating a audio warning signal from an audio module arranged in a HVAC monitoring apparatus; directing the audio warning signal into a plenum of the HVAC system; propagating the audio warning signal through an air duct network, the air duct network is in fluid communication with the plenum. 